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Materials Science 1 > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

who created the periodic table?

A

Dmitri Mendeleev

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2
Q

what was Niels Bohr’s model of the structure of an atom?

A
  • negative electrons orbit the central nucleus in discrete orbital shells
  • electrons have quantised positions and specific energies
  • stable configurations have full outer shells
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3
Q

if atoms have similar numbers of outer shell electrons what does this mean?

A

they have similar properties

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4
Q

what is the atomic number equal to?

A

no. of protons and no. of electrons

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5
Q

what is the definition of the atomic mass unit (amu)?

A

equal to 1/12 of the mass of a carbon-12 atom

in imprecise terms, one amu is the average of the proton rest mass and the neutron rest mass

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6
Q

what is the relative atomic mass equal to?

A

no. of protons and neutrons

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7
Q

what is the charge of an element?

A

0 - it has equal numbers of protons and electrons

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8
Q

how are electron orbitals filled?

A

the lowest energy state is filled first

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9
Q

what is responsible for binding the protons and neutrons together in the nucleus?

A

the strong force

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10
Q

what happens with other isotopes of carbon, for example carbon-14?

A

because they are more unstable (due to the added neutrons) they are more likely to decay (beta decay)

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11
Q

what is carbon dating?

A

we can calculate how much carbon-14 was in the atmosphere a specific time relative to now which can be used in dating - by knowing the half life and working backwards

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12
Q

what is the order of electron orbital filling?

A

1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, 4d10, 5p6, 4f14, 5d10, 6s2, 6p6

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13
Q

how do you calculate the average atomic weight of an element?

A

times each percentage abundance with the mass and add them all together

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14
Q

what was Thomson’s plum pudding model?

A

in Thomson’s model, the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons’ negative charges, like negatively charged “plums” surrounded by positively charged “pudding”

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15
Q

what model do we use today for the structure of an atom? describe it?

A

quantum mechanical model - the orbitals are where we can expect to find electrons (locations are described as probabilities) and the properties of the electrons are described using a wave equation with wave and particle like properties (like a standing wave)

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16
Q

what is the name for numbering the electron shells around the nucleus?

A

principal quantum numbers (goes up to 7)

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17
Q

how many electrons fit in the s orbital?

A

2

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18
Q

how many electrons fit in the p orbital?

A

6

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19
Q

how many electrons fit in the d orbital?

A

10

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20
Q

how many electrons fit in the f orbital?

A

14

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21
Q

what is the magnetic quantum number (mI)?

A

relates to the electron’s orientation in space - it can be …-2, -1, 0, 1, 2… and so on

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22
Q

what is the spin quantum number (ms)?

A

relates to the electron’s spin - it can be -0.5 or 0.5

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23
Q

what is the shape of an s orbital?

A

spherical

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24
Q

what is the shape of a p orbital?

A

dumbell shaped

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25
Q

what is special about the noble gases?

A

they have full outer shells, complete s and p sub-shells, they tend to be very unreactive due to their stability - it won’t form primary bonds with anything, they are inert and have low energy (group 0)

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26
Q

what is the Pauli exclusion principle?

A

this states that each electron state/orbital can hold no more than two electrons and they must have opposite spin

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27
Q

what are valence electrons?

A

valence electrons are those which occupy the outermost electron shell

28
Q

what determines an atom’s physical and chemical properties?

A

the number of valance electrons

29
Q

what is electronegativity?

A

the ability of an atom to attract electrons to itself

30
Q

what element is the most electronegative?

A

flourine

31
Q

are metals electron donors or acceptors?

A

donors

32
Q

are non-metals electron donors or acceptors?

A

acceptors

33
Q

what do the groups in the periodic table relate to?

A

elements with the same number of valance electrons, they have similar properties

34
Q

what are the 3 types of primary bonding?

A

ionic
metallic
covalent

35
Q

what are the 2 types of secondary bonding?

A

van der walls

hydrogen bonding

36
Q

which type of bonding is stronger, primary or secondary?

A

primary

37
Q

what is ionic bonding and where do you find it?

A
  • often found in ceramics like alumina Al2O3, MgO (magnesia)
  • between compounds of metal and non-metal elements e.g NaCl, AL2O3, MgO, CaF2
  • requires electron transfer and a large difference in electronegativity
  • electrostatic attractions between oppositely charged ions
  • non directional
  • relatively strong
  • high melting point
  • high elastic modulus
  • brittle (difficult for atoms to slide/rearrange)
  • electrical/thermal insulators (no free electrons)
  • crystal lattice structure
38
Q

which is positive cation or anion? and hence which is negative?

A

cation - positive ion

anion - negative ion

39
Q

what is covalent bonding and where do you find it?

A
  • occurs in polymers and some ceramics (typically non-metal compounds) for example methane CH4, H2, F2, SiC
  • the electrostatic attraction between a shared pair of electrons and the nuclei of both bonded atom
  • the two elements have similar electronegativities
  • diamond and silicon are elemental solids with covalent bonds, have larger bond energy
  • insulators because there are no free electrons
  • very strong, directional bond (brittle)
  • high melting point
  • high elastic modulus
  • less dense than ionic/metallic bonding materials (directional bonds make it harder to “pack” atoms)
40
Q

what is metallic bonding and where do you find it?

A
  • occurs in metals e.g Al, Fe, Mg or tungsten (W)
  • electrostatic attraction between positively charged ions and the sea of electrons surrounding them (valence electrons are delocalised)
  • high electrical and thermal conductivity
  • electrons are not bound to one particular atom
  • non directional, intermediate strength bond
  • ductile because the planes of atoms can slide over each other
  • intermediate melting point and elastic modulus
  • close packing of atoms (high density)
41
Q

what are the two types of van der walls bonding? what is van der walls bonding?

A
  • fluctuating/temporary dipole interactions
    between inert gases or covalent molecules e.g H2
  • permanent dipole-dipole interactions
    between molecules with permanent dipoles like HCl or polymers
42
Q

what are some characteristics of van der walls forces?

A
  • weak, smallest bond energy out of all the bond types
  • directional
  • van der walls forces hold neighbouring molecules together
  • seen in polymers between chains
  • low stiffness
  • low melting point
  • very ductile
43
Q

what is hydrogen bonding?

A
  • seen in water H2O
  • weak, secondary bond
  • occurs from the interaction and delocalisation of hydrogen electrons
44
Q

what does Fa refer to?

A

attractive force between two atoms - depends on the type of bonding/valence electrons (valence electron interacts with neighbouring positive nucleus)

45
Q

what does Fr refer to?

A

repulsive force between two atoms - depends on the overlap of electrons

46
Q

what is the equation for the net force between the atoms?

A

Fn = Fa + Fr

47
Q

when do you have the equilibrium position between two atoms?

A

when Fa + Fr = 0 (equal and opposite) which gives the length of our bond (r = r0) - here the energy is at a minimum

48
Q

is the attractive force positive or negative?

A

positive

49
Q

is the repulsive force positive or negative?

A

negative

50
Q

what are the forces between atoms a result of?

A
  • the forces result from the potential energy between the atoms
  • the FORCE is the DIFFERENTIAL of energy
  • this energy reveals fundamental properties of materials
51
Q

what is the relationship between Tm and Eo (melting point and bonding energy)?

A

Tm is larger if Eo is larger

52
Q

what is the relationship between E and Eo (stiffness/elastic modulus and bonding energy)?

A

E is larger if Eo is larger

53
Q

what is the general equation for the attractive force Fa?

A
  • A / r^2 (where A is a constant for a given bond)
54
Q

what is the general equation for the repulsive force Fr?

A

B / r^9 (where B is a constant for a given bond)

55
Q

generally, what bonding do ceramics have and what is the scale of Tm and E values?

A
  • usually ionic or covalent bonds
  • large bond energy
  • large Tm
  • large stiffness E
56
Q

generally, what bonding do metals have and what is the scale of Tm and E values?

A
  • metallic bonding
  • moderate Tm
  • moderate stiffness E
57
Q

generally, what bonding do polymers have and what is the scale of Tm and E values?

A
  • covalent and secondary

- because the secondary bonding dominates they have low Tm and low stiffness E

58
Q

how do we calculate equilibrium separation (r0) in nm? and how from this do we calculate bonding energy (E0) in eV?

A

En = Ea + Er
En = - 1.5 / r + (7x10^-6) / r^8
differentiate to get force equation
Fn = 1.5 / r^2 + (-8x7x10^-6) / r^9
Make Fn = 0 because there is 0 net force at equilibrium to find r0 in nm
substitute r0 into energy equation to get E0, bonding energy in eV

59
Q

what does the bond strength and energy determine?

A

fundamental properties such as melting point and stiffness

60
Q

what is the strength of a material dependent on?

A

dependent on defects within the material like chalk for example

61
Q

what is the structure of diamond?

A

diamond is organised in a giant covalent lattice structure with strong covalent bonds between carbon atoms, each carbon atom forms 4 bonds - tetrahedral lattice

62
Q

is silicon carbide SiC covalent or ionic?

A

covalent

63
Q

what is bronze an alloy of?

A

Cu and Sn - copper and tin

64
Q

what equations do you need to know for working out number of atoms/particles?

A 
n = M / mr (mass over Mr)
Np = n x A (Avogadro's constant)
65
Q

what is Avogadro’s constant equal to?

A

6.022x10^23 atoms

66
Q

what is the equation for % ionic character?

A

% ionic character = [1 - e^(-(0.250)(Xa - Xb)^2)] x 100
where:
Xa = electronegativity of most electronegative element
Xb = electronegativity of least electronegative element

Materials Science 1 (10 decks)

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